So-called backlights of e.g. liquid crystal displays generally have a similar construction, comprising a side-lit lightguide, and extraction features to extract the light out of the lightguide. Such backlights may e.g. be relatively flat lamps that still have a large light emitting area. Often, these backlights have to fulfill the requirement of providing lighting as homogeneously as possible, and in particular the light extraction structures are adapted to this goal.
However, a disadvantage of such backlights, or lamps of this kind in general, is that the direction of the emitted light is much less well-defined. A desirable control over lighting properties cannot be obtained with such lamps with homogeneously, yet substantially randomly, emitted light.
It is an object of the present invention to provide a flat lamp having the known advantages of the known lamp, but that in addition is able to emit light with a better-defined behavior. This better-defined behavior in turn can provide special properties hitherto not supplied by e.g. backlights.